Random access configuration for MTC operation

ABSTRACT

The present disclosure relates to methods for random access message repetition, as well as to a wireless device, and a network node executing these methods. When performed by a wireless device in a wireless network, the method comprises selecting a Random Access Channel (RACH) resource associated with a RACH configuration for random access message repetition with a pre-determined number of repetitions for a single random access attempt; and transmitting, for the single random access attempt, a random access message with the pre-determined number of repetitions using the selected RACH resource.

TECHNICAL FIELD

The disclosure relates to a random access procedure. The disclosurerelates to methods for random access message repetition, as well as to awireless device, and a network node executing these methods.

BACKGROUND

3GPP Long Term Evolution, LTE, is the fourth-generation mobilecommunication technologies standard developed within the 3rd GenerationPartnership Project, 3GPP, to improve the Universal MobileTelecommunication System, UMTS, standard to cope with futurerequirements in terms of improved services such as higher data rates,improved efficiency, and lowered costs. The Universal Terrestrial RadioAccess Network, UTRAN, is the radio access network of a UMTS and EvolvedUTRAN, E-UTRAN, is the radio access network of an LTE system. In anUTRAN and an E-UTRAN, a User Equipment, UE, is wirelessly connected to aRadio Base Station, RBS, commonly referred to as a NodeB, NB, in UMTS,and as an evolved NodeB, eNodeB or eNodeB, in LTE. An RBS is a generalterm for a network node capable of transmitting radio signals to a UEand receiving signals transmitted by a UE.

A currently popular vision of the future development of thecommunication in cellular networks comprises large numbers of smallautonomous devices, which typically transmit and receive only smallamounts of data infrequently, for instance once per week to once perminute. These devices are generally assumed not to be associated withhumans, but are rather sensors or actuators of different kinds, whichcommunicate with application servers for the purpose of configuration ofand data receipt from said autonomous devices within or outside thecellular network. Hence, this type of communication is often referred toas machine-to-machine, M2M, communication and the devices are denotedMachine Devices, MDs. The nomenclature used in 3GPP standardization forthe communication is Machine Type Communication, MTC, whereas thedevices are denoted MTC devices. As these devices are assumed totypically transmit rather seldom, their transmissions will in most casesbe preceded by a Random Access, RA, procedure, which establishes thedevice's access to a network and reveals the device's identity to thenetwork.

Internet of Things (IoT) and the related concept of Machine-TypeCommunication (MTC) is an important revenue stream for operators andhave a huge potential from the operator perspective. It is efficient foroperators to be able to serve MTC UEs using already deployed radioaccess technology. Therefore, 3GPP LTE has been investigated as acompetitive radio access technology for efficient support of MTC 3GPP TR36.888 v12.0.0. Lowering the cost of MTC UEs is an important enabler forimplementation of the IoT. Many MTC applications will require lowoperational UE power consumption and are expected to communicate withinfrequent, bursty transmissions and small-size data packets. Inaddition, there is a substantial market for the M2M use cases of devicesdeployed deep inside buildings which would require coverage enhancementin comparison to the defined LTE cell coverage footprint.

3GPP LTE Rel-12 has defined a UE power saving mode allowing long batterylifetime and a new UE category allowing reduced modem complexity. InRel-13, further MTC work is expected to further reduce UE cost andprovide coverage enhancement. The key element to enable cost reductionis to introduce reduced UE bandwidth of 1.4 MHz in downlink and uplinkwithin any system bandwidth.

In LTE the system bandwidth can be up to 20 MHz and this total bandwidthis divided into physical resource blocks (PRBs) of 180 kHz. Thelow-complexity UEs with reduced UE bandwidth of 1.4 MHz that will beintroduced in LTE Rel-13 will only be able to receive a part of thetotal system bandwidth at a time—a part corresponding to up to 6Physical Resource Blocks, PRBs, in a subframe. In the following, werefer to a group of 6 PRBs as a ‘PRB group’ or a ‘narrowband’.

In 3GPP, coverage enhancement is proposed for MTC applications. In orderto achieve the coverage targeted in LTE Rel-13 for low-complexitywireless devices and other types of wireless devices operating delaytolerant MTC applications, time repetition techniques may be used, i.e.,enabling energy accumulation of the received signals at the networknode, also known as eNB, to achieve such coverage enhancements. Forphysical data channels (PDSCH, PUSCH), subframe bundling (a.k.a. TTIbundling) can be used. When subframe bundling is applied, each HARQ(re)transmission consists of a bundle of multiple subframes instead ofjust a single subframe. Repetition over multiple subframes can also beapplied to physical control channels. Depending on a UE's coveragesituation, different number of repetitions will be used.

From the physical layer perspective, the random access procedureencompasses the transmission of a random access message, also known as arandom access preamble, and random access response. A physical randomaccess channel, PRACH, occupies 6 resource blocks in an uplink subframeor in a set of consecutive uplink subframes reserved for random accessmessage transmissions. In the context of the present disclosure, arandom access attempt may be composed of multiple repetitions of randomaccess message transmission. The number of repetitions in a randomaccess attempt is also known as a repetition level. The repetition levelis correlated to energy accumulation in the receiving eNB.

The maximum bandwidth that Rel-13 low-complexity wireless devices canread in any system is 6 Physical Resource Blocks, PRBs, in a subframe.Furthermore, Rel-13 low-complexity wireless devices often need multiplerepetitions to transmit a random access attempt. Consequently, whilecoverage enhancement through random access message repetition has beenproposed, solutions suitable or applicable for low-complexity wirelessdevices are still wanting.

Hence, there is a need to provide a random access procedure whichprovides sufficient coverage and is suitable for low-complexity wirelessdevices, such as low rate MTC devices.

SUMMARY

An object of the present disclosure is to provide solutions which seekto mitigate, alleviate, or eliminate one or more of the above-identifieddeficiencies in the art and to provide solutions improving random accessprocedures implementing random access message repetition.

This object is obtained by a method, performed in a wireless device in awireless network. The method comprises selecting a Random AccessChannel, RACH, resource associated with a RACH configuration for randomaccess message repetition with a pre-determined number of repetitionsfor a single random access attempt and transmitting, for the singlerandom access attempt, a random access message with the pre-determinednumber of repetitions using the selected RACH resource.

The disclosed method provides significant advantages by configuring RACHrandom access message transmission for low-complexity communication,e.g., Machine Type Communication, MTC, thereby enabling the wirelessdevice to perform random access attempts using multiple transmissions ofrandom access messages in a single random access attempt, so that onerandom access message transmission can be repeated multiple times andspan multiple random access message, i.e., preamble, transmissionopportunities during the single random access attempt. RACH resourcesare associated with RACH configuration indexes so that random accessmessage repetition only occurs in preamble transmission opportunitiesspecified by RACH configuration index.

According to an aspect of the disclosure, the method further comprisesreceiving information on RACH resources available for random accessmessage repetition, wherein the received information comprises anassociated RACH configuration for each RACH resource.

According to a further aspect, the received information comprisesfrequency hopping information comprising a list of RACH resourcesavailable for random access message transmission during a single randomaccess attempt and a frequency hopping period. Hence, the disclosedmethod enables frequency hopping in a single random access attempt.

According to an aspect of the disclosure, the method further comprisesdetermining a random access message transmission power based on thepre-determined number of random access message repetitions of the RACHconfiguration. Thus, the random access message power calculation isadjusted to take the number of repetitions into account.

According to an aspect of the disclosure, the method further comprisesdetermining a repetition starting point, i.e., a repetition startingpoint in time, based on the predetermined number of random accessmessage repetitions. Thus, the radio access message transmission may beinitiated at an appropriate transmission opportunity for the RACHconfiguration of the selected RACH resource. The potential startingpoint of the repetitions is determined in order to align transmissionsand receptions.

According to an aspect of the disclosure, the method further comprisesdetermining a Random Access Response window based on the transmit formatof the random access response. Thus, RACH timing for receiving a randomaccess response and associated actions in the wireless device isdefined.

According to a further aspect of the disclosure, the method furthercomprises when the single random access attempt fails, incrementing therandom access message transmission power for a retry random accessattempt and/or selecting a retry number of random access messagerepetitions greater than the pre-determined number for a retry randomaccess attempt. Accordingly, the present disclosure reveals howmechanisms for improving likelihood of success for a single randomaccess attempt.

According to an aspect of the disclosure, the random access messagecomprises a Physical Random Access Channel, PRACH, preamble.

The above mentioned object of the disclosure is also obtained by acomputer readable storage medium, having stored thereon a computerprogram which, when executed in a wireless device, causes the wirelessdevice to execute any of the above mentioned method aspects.

Likewise, the object of the disclosure is obtained by a wireless devicethat is configured for performing a random access procedure in awireless network. The wireless device comprises a communication unitconfigured to communicate with a network node in a cell of the wirelessnetwork. The wireless device further comprises processing circuitry,configured to cause the wireless device to select a Random AccessChannel, RACH, resource associated with a RACH configuration for randomaccess message repetition with a pre-determined number of repetitionsfor a single random access attempt, and to transmit, using thecommunication unit, for the single random access attempt, a randomaccess message to said wireless network with a the pre-determined numberof repetitions using the selected RACH resource.

The wireless device and the computer program enable the correspondingadvantages of those described above in relation to the method performedin a wireless device.

The object to provide solutions improving random access proceduresimplementing random access message repetition is also obtained by amethod, performed in a network node in a wireless network, forperforming a random access procedure. The method comprises associatingfor a cell of said wireless network, a first Random Access Channel,RACH, resource, with a first RACH configuration and associating, for thecell, a second RACH resource with a second RACH configuration. Themethod further comprises sending an indication of the first and secondRACH configurations, wherein at least one of said first and second RACHconfiguration indicate random access message repetition for a singlerandom access attempt.

According to an aspect of the disclosure, the random access procedure isperformed using a RACH resource associated with a RACH configuration forrandom access message repetition with a pre-determined number ofrepetitions for a single random access attempt and a repetition startingpoint is determined, for the RACH configuration, based on number ofrepetitions.

According to an aspect of the disclosure, the method further comprisesdetermining, for the RACH configuration, a Random Access Response windowbased on the repetition level, where the Random Access Response windowsize depends on the transmit format of the random access response.

The above mentioned object of the disclosure is also obtained by acomputer readable storage medium, having stored thereon a computerprogram which, when executed in a network node, causes the network nodeto execute any of the above mentioned method aspects.

Likewise, the object of the disclosure is obtained by a network nodethat is configured for performing a random access procedure in awireless network. The network node comprises a communication unitconfigured to communicate with a wireless device in a cell of thewireless network. The wireless device further comprises processingcircuitry configured to cause the network node to associate, for a cellof said wireless network, for a first Random Access Channel, RACH,resource with a first RACH configuration and to associate, for the cell,a second RACH resource with a second RACH configuration. The processingcircuitry is further configured to send, using the communication unit,an indication of the first and second RACH configurations, wherein atleast one of said first and second RACH configuration indicate randomaccess message repetition for a single random access attempt.

The method performed in a network node, the computer program and thenetwork node enable the corresponding advantages of those describedabove in relation to the method performed in a wireless device.

Objects of the present disclosure are not limited to the above-describedobjects and other objects and advantages can be appreciated by thoseskilled in the art from the following descriptions. Further, it will beeasily appreciated that the objects and advantages of the presentdisclosure can be practiced by means recited in the appended claims anda combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be more readily understood through the studyof the following detailed description of the embodiments/aspectstogether with the accompanying drawings, of which:

FIG. 1 illustrates a cell of a wireless network.

FIG. 2 illustrates the sequence of messages exchanged between a deviceand an eNodeB during a random access procedure.

FIG. 3a illustrates two preamble subsets defined for contention-basedaccess.

FIG. 3b illustrates the LTE downlink physical resource.

FIG. 3c is an illustration of random access preamble transmission in thetime-frequency domain.

FIG. 4 illustrates an overview of the signaling in a system whenperforming random access channel configuration, RACH, and selectionaccording to an exemplary embodiment of the present disclosure.

FIG. 5 is a flow chart illustrating method steps performed by a networknode according to exemplary embodiments of the present disclosure.

FIG. 6 is a flow chart illustrating method performed by a wirelessdevice according to exemplary embodiments of the present disclosure.

FIG. 7 is an illustration of radio access message configurations withmultiple transmission opportunities in a subframe for FDD.

FIG. 8 is an illustration of radio access message transmission where theradio access message is repeated multiple times over a series oftransmission opportunities, wherein frequency hopping between twonarrowbands configured for PRACH transmission is used.

FIG. 9a and FIG. 9b illustrate a wireless device.

FIG. 10a and FIG. 10b illustrate a network node.

It should be added that the following description of the embodiments isfor illustration purposes only and should not be interpreted as limitingthe disclosure exclusively to these embodiments/aspects.

DETAILED DESCRIPTION

Various example embodiments will now be described more fully withreference to the accompanying drawings in which some example embodimentsare illustrated.

The example embodiments are capable of various modifications andalternative forms. However, the disclosed embodiments, shown by way ofexample, will be detail. It should be understood that there is no intentto limit example embodiments to the particular details disclosed. On thecontrary, example embodiments are to cover all modifications,equivalents and alternatives within the scope of the claims. In thedescription, like numbers refer to like elements throughout thedescription of the figures.

The general object or idea of embodiments of the present disclosure isto address at least one or some of the disadvantages with the prior artsolutions described above as well as below. The various steps describedbelow in connection with the figures should be primarily understood in alogical sense, while each step may involve the communication of one ormore specific messages depending on the implementation and protocolsused.

Embodiments of the present disclosure relate, in general, to the fieldof configuring random access resources, in a LTE wireless network.However, it must be understood that the same principle is applicable inother wireless networks for the purpose of configuring resources forrandom access.

In the present disclosure, the term wireless device is generally used. Awireless device, or user equipment, UE, which is the term used in the3GPP specifications, referred to in this application could be anywireless device capable of communicating with a wireless network.Additionally, mobile, user terminal, mobile unit, mobile station,subscriber terminal, and remote station may be considered synonymous towireless device. Examples of such devices are of course mobile phones,smartphones, laptops and Machine to Machine, M2M, devices etc. However,one must appreciate that capability to communicate with a wirelessnetwork could be built in almost any device e.g. a car, a lamp post, ascale and so on.

In the present disclosure, the term network node is generally used. Anetwork node, or radio network node, may describe equipment thatprovides data connectivity between a network and a wireless device,e.g., an eNodeB or other type of access point or base station. The termnetwork node could also represent network equipment configured tocontribute to a random access procedure in a wireless network.

In an LTE system, an uplink resource block is a time-frequency resourceconsisting of resource elements in the form of 12 subcarriers of 15 kHzeach in the frequency domain and a number of OFDM symbols, such asDFTS-OFDM symbols, of one slot of 0, 5 ms size in the time domain, wheretwo slots equals one sub frame of 1 ms. However, in a wider sense aRandom Access preamble, in the following disclosure also denominatedrandom access message, (such as one sent by the UE in the first messageof the LTE Random Access procedure) can also be seen as a Random Accessresource, enabling separation of signals using the same time-frequencyresource.

Embodiments of the present disclosure will be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the disclosure are shown. This disclosure may, however,be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein. Like reference signs referto like elements throughout.

3GPP LTE Rel-12 has defined a UE power saving mode allowing long batterylifetime and a new UE category allowing reduced modem complexity. InRel-13, further MTC work is expected to further reduce UE cost andprovide coverage enhancement. The key element to enable cost reductionis to introduce reduced UE bandwidth of 1.4 MHz in downlink and uplinkwithin any system bandwidth.

In LTE the system bandwidth can be up to 20 MHz and this total bandwidthis divided into physical resource blocks (PRBs) a 180 kHz. Thelow-complexity UEs with reduced UE bandwidth of 1.4 MHz that will beintroduced in LTE Rel-13 will only be able to receive a part of thetotal system bandwidth at a time—a part corresponding to up to 6Physical Resource Blocks, PRBs. Here we refer to a group of 6 PRBs as a‘PRB group’ or a ‘narrowband’.

The LTE RACH Procedure

For better understanding of the proposed technique the LTE RACHprocedure will now be briefly described.

FIG. 1 schematically illustrates a cellular network 100 comprising abase station 110 and two wireless devices 120 a, 120 b, e.g. MTCdevices. In a cell 101 like the one disclosed in FIG. 1, wirelessdevices are located at different distances from the base station 110,wherein the channel characteristics vary due to different reasons e.g.distance to base station, disturbing radio sources or obstacles such asbuildings.

An ongoing study item on low cost Machine Type Communication, MTC, in3GPP Radio Access network, RAN 1 aims to enhance coverage with 20 dBcoverage enhancements (CE) for low rate MTC devices. To achieve thesecoverage enhancements multiple channels will need to be improved. Thisdisclosure aims at coverage enhancements in the random access procedurealso referred to as RACH procedure. RACH stands for random accesschannel. A RACH is intrinsically a transport channel used by mobilephones and other wireless devices. However, the term RACH is often usedas a general term referring to the random access procedure.

As an example, the random access procedure of a 3GPP Evolved PacketSystem, EPS, also known as a 3GPP Long Term Evolution/SystemArchitecture Evolution, LTE/SAE, network is briefly described below.

In 3GPP Release 11, the Long Term Evolution, LTE, random accessprocedure is a four step procedure used for initial access whenestablishing a radio link, to re-establish a radio link after radio-linkfailure, to establish uplink synchronization or as a scheduling requestif no dedicated scheduling-request resources have been configured on thePhysical Uplink Control Channel, PUCCH.

3GPP Release 11 provides for a LTE random access procedure which is usedin several situations: for initial access when establishing a radio link(moving from Radio Resource Control (RRC)_IDLE to RRC_CONNECTED state);to re-establish a radio link after radio-link failure; to establishuplink synchronization; or, as a scheduling request if no dedicatedscheduling-request resources have been configured on the Physical UplinkControl Channel, PUCCH. The 3GPP Release 11 LTE random access procedureessentially comprises four basic steps which encompass a sequence ofmessages exchanged between the terminal and the eNodeB, as generallyillustrated in FIG. 2. In FIG. 2, the four steps essentially correspondto the solid arrows, whereas the dotted arrows essentially correspond tocontrol signaling for the solid arrow step which the dotted arrowsprecede. For example, the second step is the second arrow (dotted) andthe third arrow (solid). The second arrow (dotted) tells the UE tolisten to the third arrow corresponding to the second step. Further inthe same way the fifth arrow tells the UE to listen to the fourth stepin the RA-procedure corresponding to the last arrow. These basic foursteps are briefly discussed below.

A first step in the random-access procedure comprises transmission of arandom access message, also known as a random-access preamble, on aRandom Access Channel, RACH, i.e., the Physical Random-Access Channel,PRACH. As part of the first step of the random-access procedure, theterminal randomly selects one preamble to transmit, out of one of thetwo subsets 301, 302 defined for contention-based access as illustratedin FIG. 3a . In LTE totally 64 preambles 300 are defined in each cell.Contention-based setup is used when there is a risk for collision of twoUEs accessing the same resource. The subsets used for contention freesetup 303 are used e.g. at handover, where there is no risk forcollision.

LTE uses OFDM in the downlink and DFT-spread OFDM in the uplink. Thebasic LTE downlink physical resource can thus be seen as atime-frequency grid as illustrated in 3 b, where each resource elementcorresponds to one OFDM subcarrier during one OFDM symbol interval.

Which subset to select the preamble from, is given by the amount of datathe terminal would like to, and from a power perspective can, transmiton the Physical Uplink Shared Channel, PUSCH, in the third random accessstep. A time/frequency resource to be used for these transmissions isillustrated in FIG. 3c , which is understood by reading “4G-LTE/LTEAdvanced for Mobile Broadband” by E. Dahlman et al, Academic Press,2011. The time/frequency resource 310 to be used is given by the commonPRACH configuration of the cell, which can be further limited by anoptional, UE specific mask, which limits the available random accesstransmission opportunities for the given UE. This is more thoroughdescribed in “3GPP TS 36.321 v.10.0.0. Medium Access Control (MAC)protocol specification” and “3GPP TS 36.331 v.10.3.0. Radio ResourceControl (RRC) protocol specification”.

A second step of the random access procedure comprises the Random AccessResponse. In the Random Access Response the eNodeB transmits a messageon the Physical Downlink Shared Channel, PDSCH, containing the index ofthe random-access preamble sequences the network detected and for whichthe response is valid; the timing correction calculated by therandom-access preamble receiver; a scheduling grant; as well as atemporary identify, TC-RNTI, used for further communication between theUE and network. A UE which does not receive any Random Access Responsein response to its initial random-access preamble transmission of step 1above within a pre-defined time window, will consider the random accessattempt failed, and will repeat the random access pre-ambletransmission, possibly with higher transmit power, up to a number ofmaximum of four times, before considering the entire random-accessprocedure failed.

The third step of the random access procedure serves, e.g., to assign aunique identity to the UE within the cell, C-RNTI. In this third step,the UE transmits the necessary information to the eNodeB using the PUSCHresources assigned to the UE in the Random Access Response.

The fourth and last step of the random-access procedure comprises adownlink message for contention resolution. The message of this fourthstep is also known as the RRC Connection Setup message. Based on thecontention resolution message each terminal receiving the downlinkmessage will compare the identity in the message with identitytransmitted in the third step. Only a terminal which observes a matchbetween the identity received in the fourth step and the identitytransmitted as part of the first step will declare the random accessprocedure successful, otherwise the terminal will need to restart therandom access procedure.

The UE power to use in the random access attempt is calculated accordingto a specified formula, known from “3GPP TS 36.213 v.10.6.0. Physicallayer procedures”, reproduced as Expression 1 below, with parameterscarried in the system information. If the UE does not receive aRandomAccessResponse in the second step of the procedure, the transmitpower of the following PRACH transmission is increased by a parameterdelta value up until limited by the UE maximum power:PPRACH=min{P _(CMAX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PL_(c)}_[dBm]  Expression 1:

In Expression 1, P_(CMAX,c)(i) is the configured UE transmitting poweras defined in “3GPP TS 36.213 v.10.6.0. Physical layer procedures” forsub frame i of the primary cell and PL_(c) is the downlink path lossestimate calculated in the UE for the primary cell.

Hence, there are situations where a UE is unable to access the networkdue to Random Access Channel, RACH, coverage problems, e.g. the UE hasBroadcast Control Channel, coverage and can thus measure on the cell andread the cell's system information, but the network cannot receiverandom access attempts, i.e., random access preamble transmissions, fromthe UE because the UE is power/coverage limited, and hence the receivedsignal in the network is too weak. This is the case, for example, for auser placed indoor served by a cell with high output power.

As an alternative starting from LTE Release 11, a UE can be configuredto connect to multiple cells at once, i.e. one primary cell and one orseveral secondary cells and use so called carrier aggregation. In thiscase, the user equipment is also allowed to transmit RACH requests onthe “secondary” cells, if the cells belong to different timing advancegroups. However, if a device does not support carrier aggregation withmultiple timing advance values random access is only allowed on theprimary cell.

Hence, the above described random access procedure provides insufficientcoverage.

The transmission of random access requests is generally restricted tocertain allocated time and frequency resources. In LTE Release 11communication systems, Physical Random Access, PRACH, resources can beconfigured in different ways dependent on e.g. cell size. Generally theguard and cyclic prefix, i.e. the “empty” period between the preambletransmissions, differ between the different PRACH formats and givesdifferent alternatives depending on cell size. Some formats resend thesame preamble two or more times subsequently.

As previously disclosed, time repetition techniques may be used toachieve coverage enhancements, i.e., enabling energy accumulation of thereceived signals. For physical data channels, subframe bundling may beused. Repetition over multiple subframes can also be applied to physicalcontrol channels. Depending on the coverage situation, different numberof repetitions will be applied to the physical control channels

From the physical layer perspective, the L1 random access procedureencompasses the transmission of random access preamble and random accessresponse. The remaining messages are scheduled for transmission by thehigher layer on the shared data channel and are not considered part ofthe L1 random access procedure. A physical random access channel (PRACH)occupies 6 resource blocks in an uplink subframe or set of consecutiveuplink subframes reserved for random access message transmissions.

Hence, in present systems different configurations are used fordifferent cells, see also 3GPP TS 36.211 V11.0.0 (2012-10)—section 5.7.For frame structure type 1 (i.e., FDD) with PRACH preamble format 0-3,there is at most one random access resource per subframe. TS 36.211Table 5.7.1-2 lists the preamble formats and the subframes in whichrandom access preamble transmission is allowed for a given configurationin frame structure type 1 (i.e., FDD). Similar PRACH configurationexists for frame structure type 2 (i.e., TDD).

TABLE 1 (from TS 36.211v12.3.0, Table 5.7.1-2: Frame structure type 1random access configuration for preamble formats 0-3) PRACH SystemConfiguration Preamble frame Subframe Index Format number number 0 0Even 1 1 0 Even 4 2 0 Even 7 3 0 Any 1 4 0 Any 4 5 0 Any 7 6 0 Any 1, 67 0 Any 2, 7 8 0 Any 3, 8 9 0 Any 1, 4, 7 10 0 Any 2, 5, 8 11 0 Any 3,6, 9 12 0 Any 0, 2, 4, 6, 8 13 0 Any 1, 3, 5, 7, 9 14 0 Any 0, 1, 2, 3,4, 5, 6, 7, 8, 9 15 0 Even 9 16 1 Even 1 17 1 Even 4 18 1 Even 7 19 1Any 1 20 1 Any 4 21 1 Any 7 22 1 Any 1, 6 23 1 Any 2, 7 24 1 Any 3, 8 251 Any 1, 4, 7 26 1 Any 2, 5, 8 27 1 Any 3, 6, 9 28 1 Any 0, 2, 4, 6, 829 1 Any 1, 3, 5, 7, 9 30 N/A N/A N/A 31 1 Even 9 32 2 Even 1 33 2 Even4 34 2 Even 7 35 2 Any 1 36 2 Any 4 37 2 Any 7 38 2 Any 1, 6 39 2 Any 2,7 40 2 Any 3, 8 41 2 Any 1, 4, 7 42 2 Any 2, 5, 8 43 2 Any 3, 6, 9 44 2Any 0, 2, 4, 6, 8 45 2 Any 1, 3, 5, 7, 9 46 N/A N/A N/A 47 2 Even 9 48 3Even 1 49 3 Even 4 50 3 Even 7 51 3 Any 1 52 3 Any 4 53 3 Any 7 54 3 Any1, 6 55 3 Any 2, 7 56 3 Any 3, 8 57 3 Any 1, 4, 7 58 3 Any 2, 5, 8 59 3Any 3, 6, 9 60 N/A N/A N/A 61 N/A N/A N/A 62 N/A N/A N/A 63 3 Even 9

A random access configuration specifies the time and frequency ofassociated downlink resources. The configuration includes all time slotson a certain frequency f1, or a selected number of frequencies on acarrier f1.

FIG. 4 is a combined signaling diagram and flowchart showing an overviewof the signaling in a system 100, comprising a wireless device 120 andnetwork node 110, when performing the random access channelconfiguration and selection according to some embodiments of thetechnology disclosed herein. More specifically, FIG. 4 discloses anoverview of the messages going between the wireless device 120 and thenetwork node 110.

The network node 110, further described in FIG. 10a and FIG. 10b , ise.g. a base station node, also simply known as “base station”.

The network node 110 comprises a communication unit 112 through whichthe network node 110 communicates on both uplink (UL) and downlink (DL)with the wireless device 120 over a radio or air interface 401. Theradio or air interface 401 is illustrated by a dashed-dotted line inFIG. 4. In similar manner, the wireless device, further described inFIG. 9a and FIG. 9b , also comprises a communication unit 122.

As schematically disclosed in FIG. 4, the RACH configurations forrespective RACH resources, e.g., frequency resources also referred to asnarrowband resources or narrowbands, are provided by the network node110 and indications of the RACH configurations are sent, e.g.,broadcasted in a System Information Broadcast, SIB, message, to one ormore wireless device 120 in a cell defined by the network node. Thewireless device selects a RACH resource associated with a RACHconfiguration and transmits a random access attempt using the selectedRACH resource. In the context of the present disclosure, the terminologyof RACH resource, frequency resource, narrowband or PRACH resource areused interchangeably to represent resources applicable for random accessmessage transmission, i.e., random access preamble transmission.

Turning to FIGS. 5 and 6, method steps performed by the network node 110and the wireless device 120 respectively for the proposed random accessprocedure are disclosed. In the presentation below, a general outline ofthese method steps performed in the respective nodes will first bepresented followed by a discussion focusing on aspects of the randomaccess procedure as a whole. In the following disclosure, PRACHconfiguration index and RACH configuration indexes will be discussedinterchangeably. More specifically, PRACH configuration index denotes arepresents a configuration index within the general denomination of RACHconfiguration index. Likewise, PRACH configuration denotes aconfiguration within the general denomination RACH configuration.

FIG. 5 discloses a method performed in a network node 110 in a wirelessnetwork 100 for performing a random access procedure. The methodcomprises associating S1 for a cell of said wireless network, a firstRandom Access Channel, RACH, resource, with a first RACH configuration,and associating S2 for the cell, a second RACH resource, with a secondRACH configuration. Following the association, the network nodes, sendsS3, in the cell, an indication of the first and second RACHconfigurations, wherein at least one of said first and second RACHconfiguration is configured for random access message repetition for asingle random access attempt. In the context of the present disclosure,it will be understood that, although the terms first and second are usedherein to distinguish between various configurations and resourceelements, such configurations and resources are not limited by theseterms. First and second are only used to distinguish the respectiveconfigurations and resources, and a first configuration could just aswell be denominated as a second configuration, without departing fromthe scope of example embodiments. Also, the disclosure is not limited touse of two configurations or RACH resources, the disclosed principle isequally applicable to any number of configurations or RACH resources. Afurther discussion on such configurations and resources will followbelow.

FIG. 6 discloses wireless device aspects associated with the randomaccess procedure of FIG. 5. The wireless device selects S11 a RandomAccess Channel, RACH, resource associated with a RACH configuration forrandom access message repetition with a pre-determined number ofrepetitions for a single random access attempt. For the single randomaccess attempt, a random access message is transmitted S14 with thepre-determined number of repetitions using the selected RACH resource.

According to an aspect of the disclosure, the wireless device receivesS10 information on RACH resources available for random access messagerepetition, wherein the received information comprises an associatedRACH configuration for each RACH resource. Such information may beretrieved from the indications on RACH configurations, e.g., first andsecond RACH configurations, sent S3 by the network node. The RACHresources are, according to an aspect of the disclosure, selected basedon channel quality measurements and appropriate RACH configurations forthe predetermined number of repetitions.

Further details on RACH configuration and aspects relating to thepre-determined number of repetitions will be detailed below.

Random Access Channel Resources and Configuration

As discussed above, a maximum bandwidth of low-complexity wirelessdevice is 6 Physical Resource Blocks, PRBs in a subframe. Aspects ofthis disclosure propose that multiple narrowbands of 6 PRB can bedefined. In other words, in one cell, there are several available narrowfrequency resources that may be used depending on network conditions.Such narrowband frequency resource represents a RACH resource. In thefollowing disclosure, RACH narrowband, narrowband, frequency resourceand RACH resource may be used interchangeably. A RACH resource maycomprise e.g. allocated resource elements (RE) in a time frequencydomain as illustrated in FIG. 3b . The RACH resources may be used fortransmission of a random access preamble and/or repetition of a randomaccess preamble, by a wireless device. Multiple different RACH resourcesmay be allocated for a cell. For each RACH resource there will be aseparate random access channel configuration, RACH. Random accesschannel, RACH, configuration in this disclosure refers to theconfiguration of RACH resources and comprises e.g., RACH and PRACHconfiguration index and repetitions and settings for frequency hopping.

According to some aspects, this disclosure relates to a method performedfor performing a random access procedure in a wireless network. Aspreviously disclosed, this method comprises associating S1 in a cell ofsaid wireless network, a first Random Access Channel, RACH, resource,with a first RACH configuration and associating S2 in the cell, a secondRACH resource, with a second RACH configuration, wherein said first andsecond random access channel configuration, RACH, have different RACHconfiguration indexes and/or random access message repetition levels.The RACH resources are e.g. narrow frequency resources of e.g. 1.4 MHz,also denominated narrowbands or frequency resources in the context ofthe present disclosure. A repetition level corresponds to a number ofrepetitions, i.e., a pre-determined number of repetitions. For example,there may be 3 repetition levels defined, where the 1st repetition levelcorresponds to 5 repetitions, 2nd repetition level corresponds to 10repetitions, and the 3rd repetition level corresponds to 20 repetitions.

In the following, RACH configuration and PRACH configuration will bediscussed; PRACH configuration denoting a configuration within thedenomination RACH configuration.

The PRACH configuration of 1st narrowband can be the same as legacy UE,and has no preamble repetition. This is e.g. used by MTC devices closeto the eNodeB.

PRACH configuration of 2nd narrowband can be different, taking intoconsideration the coverage enhancement (CE) level the cell supports,load, etc.), and it includes preamble repetition.

Similarly, for the j-th narrowband configured for PRACH transmission,PRACH configuration of j-th narrowband can have its own PRACHconfiguration index and preamble repetition level.

The method further comprises sending S3, in the cell, an indication ofthe first and second RACH configurations, wherein at least one of saidfirst and second RACH configuration indicate random access messagerepetition for a single random access attempt.

In general, a cell with large bandwidth and higher load uses PRACHconfiguration of more available transmission opportunities. Sincewireless device with high repetition level costs more transmissionopportunities, wireless devices of different repetition level should usedifferent RACH resources having respective RACH configurations.

Considering, the disclosure from FIG. 6 again, a RACH resource having aRACH configuration for random access message repetition with apre-determined number of repetitions of a single random access attemptis selected S11 and the random access message is transmitted S14 withthe predetermined number of repetitions for the single random accessattempt using the selected RACH resource.

According to an aspect of the disclosure, the RACH resource is selectedbased on channel quality measurements and appropriate RACH configurationfor the pre-determined number of repetitions; assigning the wirelessdevice to a specific RACH resource.

According to a further aspect of the disclosure, the wireless devicereceives S10 information, e.g., in an indication sent from the networknode, on RACH resources available for random access message repetition,wherein the received information comprises an associated RACHconfiguration for each RACH resource. Indications sent from the networknode may be broadcasted in a System Information Block, SIB.

As mentioned, wireless device of different repetitions level should usedifferent PRACH configurations. For example:

-   -   A wireless device that requires no preamble repetition can be        assigned to 1st narrowband/RACH resource. The 1^(st) narrowband        can be a RACH resource shared with legacy wireless devices;    -   A wireless device that requires 2-10 preamble repetitions can be        assigned to a 2^(nd) narrowband/RACH resource. The second        narrowband has relatively frequent RACH transmission        opportunity, for example, 2 subframes for every radio frame;    -   A wireless device that requires 11-20 preamble repetitions can        be assigned to a 3rd narrowband/RACH resource. The 3rd        narrowband has more frequent RACH transmission opportunity than        2^(nd) narrowband, for example, 5 subframes for every radio        frame;    -   A wireless device that requires more than 20 preamble        repetitions can be assigned to a 3rd narrowband/RACH resource.        The 4th narrowband has the most frequent RACH transmission        opportunity, for example, every subframe (i.e., 10 subframes)        for every radio frame.

FIG. 7 illustrates the preamble transmission opportunities over multiplePhysical Random Access Channels, PRACH, using the following as anexample:

-   -   FDD    -   3 UL narrowbands for PRACH transmission opportunity:        -   For the first narrowband (upper row) PRACH Configuration            Index=3 (see table above), and it is intended for wireless            devices with single preamble transmission (i.e., no            repetition). This narrowband can also be shared with legacy            UE.        -   For the second narrowband (middle row): PRACH Configuration            Index=7, and it is intended for wireless devices with 4            repetitions for a preamble transmission. Alternatively this            narrowband can be used by wireless devices with frequency            hopping period of 4 repetitions, i.e., the wireless device            stays at a given narrowband for 4 preamble transmission            opportunities before switching to another narrowband.        -   For the third narrowband (lower row): PRACH Configuration            Index=12, and it is intended for wireless devices with 10            repetitions for a preamble transmission. Alternatively this            narrowband can be used by wireless devices with frequency            hopping period of 10 repetitions, i.e., the wireless device            stays at a given narrowband for 10 preamble transmission            opportunities before switching to another narrowband.

The different PRACH configurations can also be mapped to the samenarrowband(s). In this case wireless devices with different repetitionlevels are distinguished by their use of different PRACH sequences (codemultiplexing).

Frequency hopping between two or more RACH/PRACH resources may also beapplied. According to aspects of the present disclosure, the informationreceived by the wireless device, further comprises frequency hoppinginformation, e.g., a list of RACH resources available for random accessmessage transmission during a single random access attempt and afrequency hopping period.

For example the wireless device could transmit X repetitions of thepreamble within one narrowband, then hop to a second narrowband totransmit X repetitions, and then hop back to the first narrowband totransmit X repetitions, and so on until all repetitions have beentransmitted. Each wireless device can randomly select which narrowbandto use as the initial narrowband to transmit preamble on, so that PRACHcollision between wireless devices using the same set of PRACHnarrowband can be reduced. While not necessary, it is preferable thatPRACH narrowbands grouped for a frequency hopping pattern share the samePRACH configuration index so that radio access message transmissiontiming is simple.

FIG. 8 illustrates frequency hopping of preamble transmission withmultiple repetitions. The wireless device hops between two narrowbands,when transmitting radio access messages, also known as preambles. Firstsome preambles are transmitted on one narrowband, and then somepreambles are transmitted on another. In FIG. 8, the wireless devicetransmits 4 repetitions of the preamble within a narrowband beforeswitching to another narrowband and frequency hopping patterns forpreamble transmission of two wireless devices are multiplexed in timeand frequency.

The eNB broadcasts at least the following in a system information block(SIB) for MTC PRACH configuration:

-   -   List of narrowband available for preamble transmission of MTC        UE; the narrowband info provides frequency location of preamble        transmission within UL system bandwidth. The PRACH narrowband is        6 PRB in size. The narrowband can be specified via either (a)        narrowband index or (b) frequency offset in terms of PRB.    -   List of PRACH Configuration Index, one for each PRACH narrowband        described above.    -   Frequency Hopping info:        -   If frequency hopping of PRACH is enabled or not;        -   If frequency hopping of PRACH is enabled a hopping pattern            comprising:            -   A list of narrowband the UE may hop to;            -   The frequency hopping period X.

Repetition Starting Point

Since a random access attempt is composed of multiple random accessmessage repetitions, there is a need to define the allowed startingpoint (radio frame index and/or subframe index) of each random accessattempt. In other words, the wireless device and network node need toknow which the first is and which is the last preamble repetition thatcan be combined.

This could be done for each narrowband in the previous example or itcould be done for only one narrowband.

In a network node wherein the random access procedure is performed usinga RACH resource having a RACH configuration for random access messagerepetition with a pre-determined number of repetitions for a singlerandom access attempt, a repetition starting point may be determined S4based on number of repetitions. According to an aspect of thedisclosure, determination of a repetition starting point may also beperformed in the wireless device, i.e., the wireless device determinesS13 a a repetition starting point based on the pre-determined number ofrandom access message repetitions. As will be further discussed below,the repetition starting point may be determined as a system framenumber, SFN. In the following presentation N_(PRACH,rep) is the numberof repetitions of a random access message format for a given randomaccess attempt.

For the purpose of determining a repetition starting point, the conceptof a PRACH density value is introduced, the PRACH density value,D_(RA,t), being a number of PRACH transmission opportunities for a PRACHconfiguration.

If the PRACH resource is reoccurring in all radio frames, the set ofpossible starting radio frames have SFN (System Frame Number):SFN_(PRACH,start) =j*ceiling(N _(PRACH,rep) /D _(RA,t))where j, j>=0, is an integer, N_(PRACH,rep) is the number of repetitionsof an existing preamble format for the given random access attempt,D_(RA,t) is the PRACH density value in time which is equal to the totalnumber of preamble transmission opportunities at a given uplink, UL,narrowband, within a given period of time, when repetition is not used.Typically, D_(RA,t) is counted for a single narrowband within a radioframe (i.e., 10 ms) where the radio frame is available for PRACHaccording to the PRACH Configuration. D_(RA,t) does not count differenttransmission opportunities in different narrowbands within a subframe.The ceiling functions map a real number to the smallest followinginteger.

Typically, for Rel-13 MTC, a given narrowband is a given set of 6contiguous PRBs. For example, in FIG. 7, the uppermost narrowband hasD_(RA,t)=1, the second narrowband has D_(RA,t)=2, the 3rd narrowband hasD_(RA,t)=5.

If the PRACH resource is reoccurring in even radio frames, D_(RA,t) iscounted for a single narrowband within an even-indexed radio frameaccording to the PRACH Configuration. The set of possible starting radioframes have SFN:SFN_(PRACH,start)=2*j*ceiling(N _(PRACH,rep) /D _(RA,t))

If the PRACH resource is reoccurring in odd radio frames, D_(RA,t) iscounted for a single narrowband within an odd-indexed radio frameaccording to the PRACH Configuration. The set of possible starting radioframes have System Frame Number, SFN:SFN_(PRACH,start)=2*j*ceiling(N _(PRACH,rep) /D _(RA,t))+1

A wireless device procedure may be defined as follows.

-   -   Step 1. For a given PRACH configuration Index, the wireless        device determines a N_(PRACH,rep) value for the random access        attempt.    -   Step 2. Then the wireless device determines the set of possible        starting radio frames SFN_(PRACH,start).    -   Step 3. The wireless device randomly selects a starting radio        frame index from the set of possible radio frames to start the        PRACH preamble transmission.

Corresponding calculations may be done both in the network node and inthe wireless device. According to aspects of the disclosure, thewireless device determines a repetition starting point (in terms ofradio frame index) based on number of repetitions for a given randomaccess attempt and density value associated with the selected RACHresource.

Thus, the above disclosed procedure specifies in what subframes a firstrandom message transmission of a random access attempt may betransmitted, i.e., the subframes wherein PRACH repetitions may start.The repetition starting point may be expressed in the form of frame orsubframe numbers and depend on the number of PRACH repetitionsN_(PRACH,rep). The definition of a repetition starting point is anenabler for performing random access with multiple transmission of arandom access message during the random access attempt, i.e.,transmission of pre-determined number of random access messages using aselected RACH resource.

Random Access Attempt Power Setting

The power of the random access message transmission, also referred to aspreamble power (P_(PRACH)) relates to the output power level thewireless device uses to transmit a random access message, i.e., a RACHpreamble.

The initial power setting is based on open-loop estimation with fullcompensation for the path-loss. This is designed to ensure that thereceived power of the random access messages is independent of thepath-loss. The wireless device estimates the path-loss by averagingmeasurements of the downlink Reference Signal Received Power (RSRP). Thebasis for setting the transmission power of a random access message,i.e., a random-access preamble, is a downlink path-loss estimateobtained from measuring on the cell-specific reference signals. Fromthis path-loss estimate, the initial transmission power is obtained.

In prior art, for each Random Access Preamble transmission, the MAClayer determines a PREAMBLE_RECEIVED_TARGET_POWER as follows:PREAMBLE_RECEIVED_TARGET_POWER=preambleInitialReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_TRANSMISSION_COUNTER−1)*powerRampingStep;  (1)

According to aspects of the present disclosure, the repetition level isconsidered for the power setting, the wireless device determining S12 arandom access message transmission power based on the pre-determinednumber of random access message repetitions of the RACH configuration.

This implies e.g. that the wireless device selects S11 a random accesschannel configuration (with an associated repetition level) andassociated RACH resource and determines S12 a random access messagetransmission power based on the number of random access messagerepetitions of the selected configuration.

According to one example preamble transmission power P_(PRACH) isdetermined as:P _(PRACH)=min{P _(cmax,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PL _(c) −P_(RAlevel)}_[dBm],   (2)where P_(CMAX,c)(i) is the configured UE transmit power for subframe iof serving cell c and PL_(c) is the downlink path loss estimatecalculated in the UE for serving cell c.

The proposed power offset, taking repetitions into account is e.g.:P _(RAlevel)=10 log 10(N _(PRACH,rep)),where N_(PRACH,rep) is the number of repetitions the UE uses to transmitthe given PRACH. The UE determines the PRACH repetition level NPRACH,repaccording to RSRP/RSRQ measurement. For example, M possible values ofNPRACH,rep can be predefined, NPRACH,rep,set=[5, 10, 20, 40, 60, 80],and the UE selects the appropriate NPRACH,rep for initial random accessattempt.

The wireless device is configured to monitor S15 a Random AccessResponse window for one or more responses to the single random accessattempt, and to transmit S14, for a retry random access attempt, arandom access message with a retry number of repetitions when the singlerandom access attempt fails.

Thus, when a random access attempt fails, the wireless device may retrywith another preamble transmission performing S16 one or both of thefollowing for the retry random access attempt: incrementing S16 a therandom access message transmission power and/or selecting S16 b a retrynumber of repetitions greater than the pre-determined number ofrepetitions.

In one variant, the PREAMBLE_TRANSMISSION_COUNTER is incremented by 1,resulting in a higher PREAMBLE_RECEIVED_TARGET_POWER. Thus the UE canretry with a higher transmission power.

In another variant, the UE can select a new, higher NPRACH,rep, for theretry, without increasing PREAMBLE_RECEIVED_TARGET_POWER. Let theinitial random access attempt have PREAMBLE_TRANSMISSION_COUNTER=1, andNPRACH,rep=NPRACH,rep,set(i0) repetitions. WhenPREAMBLE_TRANSMISSION_COUNTER is incremented, it causes the UE to usethe next higher NPRACH,rep but the same PREAMBLE_RECEIVED_TARGET_POWERas the previous random access attempt. That is, for the second randomaccess attempt, PREAMBLE_TRANSMISSION_COUNTER=2, andNPRACH,rep=NPRACH,rep,set(i0+1). In general, as the UE re-attemptsrandom access, the UE use the number of repetitions:NPRACH,rep=NPRACH,rep,set(i0+PREAMBLE_TRANSMISSION_COUNTER−1)  (3)

This is useful for MTC UE since Rel-13 MTC UE is expected to have lowmaximum transmit power. When the MTC UE changes the repetition level ofpreamble transmission, it may also change other parameters of preambletransmission, including preamble sequence, UL narrowband index,frequency hopping pattern, etc. For example, tune to a differentnarrowband which corresponds to the new repetition level.

In yet another variant, the UE can increase both NPRACH,rep andPREAMBLE_RECEIVED_TARGET_POWER. For example, the UE can increasetransmission power according to (1). When the criteria for increasingrepetition level is reached (e.g., when maximum transmission power isreached or a number of preamble attempts is reached), the UE thenincreases number of repetitions according to (3).

According to an aspect of the disclosure, the retry random accessattempt is a next random access attempt or a periodically re-occurringsub-Sequent retry random access attempt.

Consequently, in a variant, the UE does not increase NPRACH,rep and/orPREAMBLE_RECEIVED_TARGET_POWER at every retry but only at every Nthretry and re-uses the last value for NPRACH,rep and/orPREAMBLE_RECEIVED_TARGET_POWER for the other retries at the samerepetition level. N may be a fixed constant or a configurable parameter(e.g. indicated in the broadcasted system information). N may be thesame or different for different repetition levels.

Thus, the above disclosed procedure for random access power settingprovides the ability to adapt the power setting to a repetition levelselected for the random access procedure and to increase the powersetting when a random access attempt fails, thereby improving thecoverage enhancement aspects of the proposed random access procedure inthat further power accumulation is enabled at the side of the wirelessdevice.

Random Access Transmission Timing

For the L1 random access procedure, the wireless devices s uplinktransmission timing after a random access preamble transmission is asfollows.

-   -   a) If a random access response, RAR, with associated RA-RNTI,        Random Access-Radio Network Temporary Identifier, is detected,        the RAR is a response to the transmitted random access message,        i.e., preamble sequence, and the last subframe containing        repetition for RAR transmission is subframe n, the wireless        device shall, according to the information in the response,        transmit an UL-SCH transport block in the first subframe n+k₁,        k₁≥6, if the UL delay field above is set to zero where n+k₁ is        the first available UL subframe for PUSCH transmission, where        for TDD serving cell, the first UL subframe for PUSCH        transmission is determined based on the UL/DL configuration        (i.e., the parameter subframeAssignment) indicated by higher        layers. The wireless device shall postpone the PUSCH        transmission to the next available UL subframe after n+k₁ if the        field is set to 1.        -   1. Note that in the above, the last subframe n for RAR            transmission could be:            -   i. Last subframe of M-PDCCH repetition, if the M-PDCCH                DCI carries the RAR message;            -   ii. Last subframe of PDSCH repetition, with or without                an M-PDCCH scheduling the PDSCH, if the PDSCH transport                block carries the RAR message.    -   b) If a random access response is received by subframe n, where        subframe n is the last subframe containing repetition for the        RAR transmission, and the DL transmission does not contain a        response to the transmitted preamble sequence, the wireless        device shall, if requested by higher layers, be ready to make        another random access attempt no later than in subframe n+k₂.        Typically k₂=5. The preamble transmission, with repetition        starts in the first preamble transmission opportunity of first        available radio frame SFN_(PRACH,start).        -   1. Note that in the above, the corresponding DL transmission            could be:            -   i. M-PDCCH DCI transmission, if the M-PDCCH DCI carries                the RAR message;            -   ii. PDSCH transport block transmission, with or without                an M-PDCCH scheduling the PDSCH, if the PDSCH transport                block carries the RAR message.        -   2. Note that in the above, the random access attempt            comprises transmitting a new preamble sequence with            N_(PRACH,rep) number of repetitions. Preferably the preamble            repetitions occur only in subframes that contain legacy            (i.e., not repeated) preamble transmission opportunity.    -   c) If no random access response is received by subframe n, where        subframe n is the last subframe containing M-PDCCH repetition in        the random access response window, the UE shall, if requested by        higher layers, be ready to transmit a new preamble sequence no        later than in subframe n+k₃. Typically k₃=4.    -   d) In case a random access procedure is initiated by a “PDCCH        order” in where the subframe n is the last subframe containing        repetition of the M-PDCCH carrying the order, the UE shall, if        requested by higher layers, transmit random access preamble in        the first subframe n+k₂, k₂≥6, where a PRACH resource is        available. Here the first available PRACH resource is the first        preamble opportunity of first available radio frame        SFN_(PRACH,start).

Random Access Response Window Size

According to some aspects the disclosure comprises determining S5, forthe RACH configuration, a Random Access Response window based on therepetition level, where the Random Access Response window size dependson the transmit format of the random access response.

The wireless device monitors random access response in in the RAResponse window. For UEs using PRACH with repetition,ra-ResponseWindowSize is interpreted to be the number of random accessresponse opportunities, where each random access response opportunityincludes the total number of subframes needed for M-PDCCH repetitionand/or PDSCH repetition corresponding to a single RAR transmission.

The absolute length of RA response window size is a function of RACHrepetition level. Let a single random access attempt spans R subframes,then the absolute length of RA response window spans(R*ra-ResponseWindowSize) subframes regardless of possible occurrence ofmeasurement gap.

-   -   When RAR is carried by M-PDCCH-scheduled PDSCH, R=Rc, where Rc        is the number of repetitions used by M-PDCCH; Note that in this        case, for the last possible attempt, the PDSCH part falls        outside of the RA Response Window, but the M-PDCCH part (which        is what UE monitors) is contained in the RA Response Window.    -   When RAR is carried by M-PDCCH DCI, R=Rc, where Rc is the number        of repetitions used by M-PDCCH;    -   When RAR is carried by M-PDCCH-less PDSCH, R=Rd, where Rd is the        number of repetitions used by the PDSCH.

In Release 8 of LTE time/frequency resources for random access, herereferred to as “RACH resources”, are indicated in the broadcasted systeminformation. The term “RACH resources” here refers to both physicalresources, i.e. frequencies and time slots, of the physical RACH, PRACH,as well as the preambles.

Turning now to FIG. 9a a schematic diagram illustrating some modules ofan exemplary embodiment of the wireless device 120 will be described. Awireless device referred to in this application could be any userequipment capable of communicating with a mobile communication network.Examples of such devices are of course mobile phones, smartphones,laptops and Machine to Machine, M2M, devices etc. However, one mustappreciate that capability to communicate with a multi-hop network couldbe built in almost any device e.g. a car, a lamp post, a scale and soon.

The wireless device 120 comprises a communication unit 122 configured tocommunicate with a network node in a cell of a wireless network. Thewireless device also comprises processing circuitry 121 arranged forselecting a Random Access Channel, RACH, resource associated with a RACHconfiguration for random access message repetition with a pre-determinednumber of repetitions for a single random access attempt; andtransmitting, using the communication unit 122, for the single randomaccess attempt, a random access message to said wireless network with athe pre-determined number of repetitions using the selected RACHresource. According to an aspect of the disclosure, the processingcircuitry 121 comprises a controller or a processor 123 a that may beconstituted by any suitable Central Processing Unit, CPU,microcontroller, Digital Signal Processor, DSP, etc., capable ofexecuting computer program code. The computer program may be stored in amemory (MEM) 123 b. The memory 123 b can be any combination of a ReadAnd write Memory, RAM, and a Read Only Memory, ROM. The memory 123 b mayalso comprise persistent storage, which, for example, can be any singleone or combination of magnetic memory, optical memory, or solid statememory or even remotely mounted memory.

When the above-mentioned computer program code is run in the processingcircuitry 121 of the wireless device 120 it causes the wireless deviceto perform the methods of any of the embodiments described above andbelow.

According to some aspects the wireless device 120 comprises modulesconfigured to perform the methods described above, see FIG. 9b . Themodules are implemented in hardware or in software or in a combinationthereof. The modules are according to one aspect implemented as acomputer program stored in a memory 123 b which run on the processingcircuitry 121 being a CPU. According to some aspects, the modules arelogical circuits in the processing circuitry 121.

The wireless device 120 comprises a resource selection module 901configured to select a Random Access Channel, RACH, resource associatedwith a RACH configuration for random access message repetition with apre-determined number of repetitions for a single random access attempt;and a transmitter module 904 configured to transmit, for the singlerandom access attempt, a random access message to the wireless networkwith a predetermined number of repetitions using the RACH resource.

According to some aspects the wireless device 120 comprises a determinermodule 902 configured to determine a random access message transmissionpower based on the pre-determined number of random access messagerepetitions of the selected configuration.

According to some other aspects, the wireless device 120 comprises adeterminer module 903 configured to determine a random access messagerepetition starting point (in terms of radio frame index and/or subframeindex) based on number of repetitions (e.g. of an existing random accessmessage format/for the given random access attempt) and density value ofrandom access message transmission opportunity associated with aselected RACH resource. According to another aspect, the determinermodule 903 may also be configured to determine a Random Access Responsewindow based on the transmit format of the random access response.

According to some aspects the wireless device 120 comprises aconsideration module 906 configured to, when the random access attemptfails, for further random access attempts performing one or both of thefollowing for the next random access attempt: (a) incrementing preamblepower and/or (b) increase repetition level.

According to another aspect, the wireless device also comprises amonitoring module 905, configured to monitor the Random Access Responsewindow for one or more response to the single random access attempt.

Turning now to FIG. 10a , a schematic diagram illustrating some modulesof an exemplary embodiment of a network node 110 will be described. Thenetwork node 110 may be implemented as an Evolved Node B (eNB or eNodeB)in LTE, but may also be implemented in the radio access technologyGlobal System for Mobile communications, GSM or Universal MobileTelecommunications System or WiMax. The network node 110 furthercomprises a communication interface (i/f) 112 arranged for wirelesscommunication with other devices or nodes, such as the wireless device120. The network node 110 also comprises processing circuitry 111arranged for associating for a cell of said wireless network, a firstRandom Access Channel, RACH, resource, with a first RACH configuration,and associating for the cell, a second RACH resource, with a second RACHconfiguration. The processing circuitry 111 is further configured forsending in the cell, using the communications unit, an indication of thefirst and second RACH configurations, wherein at least one of said firstand second RACH configuration indicate random access message repetitionfor a single random access attempt.

According to an aspect of the disclosure, the processing circuitrycomprises a controller (CTL) or a processor 113 a that may beconstituted by any suitable Central Processing Unit, CPU,microcontroller, Digital Signal Processor, DSP, etc., capable ofexecuting computer program code. The computer program may be stored in amemory (MEM) 113 b. The memory 113 b can be any combination of a ReadAnd write Memory, RAM, and a Read Only Memory, ROM. The memory 113 b mayalso comprise persistent storage, which, for example, can be any singleone or combination of magnetic memory, optical memory, or solid statememory or even remotely mounted memory. When the above-mentionedcomputer program code is run in the processor 113 a of the network node110, it causes the network node 110 it causes the network node 110 toperform the methods of any of the embodiments described above and below.

According to some aspects the network node 110 comprises modulesconfigured to perform the methods described above, see FIG. 10b . Themodules are implemented in hardware or in software or in a combinationthereof. The modules are according to one aspect implemented as acomputer program stored in a memory 113 b which run on the processor 113a being a CPU. According to some aspects, the modules are logicalcircuits in the processor 113 b.

The network node 110 comprises a first Random Access Channel, RACH,configuration module 1001 configured to configure for a first RACHresource a first RACH configuration in a cell of the wireless network.The network node 110 further comprises a second RACH configurationmodule 1002 configured to configure, for a second RACH resource, asecond RACH configuration in a cell of the wireless network. A sendermodule 1003 is configured to send, an indication of the first and secondRACH configurations, wherein at least one of said first and second RACHconfiguration is configured for random access message repetition for asingle random access attempt.

According to some aspects the network node 110 comprises a determiner1004 configured to determine, for the first random access channelconfiguration, RACH, a random access message repetition starting point(e.g. in terms of radio frame index or subframe index) for a singlerandom access attempt based on number of repetitions (e.g. of anexisting random access message format/for the given random accessattempt) and density value of random access message transmissionopportunity associated with a selected RACH resource.

According to some aspects the network node 110 comprises a windowdeterminer module 1005 configured to determine, for the first RACHconfiguration, a Random Access Response window based on the repetitionlevel, where the Random Access Response window size depends on thetransmit format (i.e. control+data for RAR, or control-only for RAR, ordata-only for RAR) of the random access response.

In the drawings and specification, there have been disclosed exemplaryaspects of the disclosure. However, many variations and modificationscan be made to these aspects without substantially departing from theprinciples of the present disclosure. Thus, the disclosure should beregarded as illustrative rather than restrictive, and not as beinglimited to the particular aspects discussed above. Accordingly, althoughspecific terms are employed, they are used in a generic and descriptivesense only and not for purposes of limitation.

The description of the example embodiments provided herein have beenpresented for purposes of illustration. The description is not intendedto be exhaustive or to limit example embodiments to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of various alternativesto the provided embodiments. The examples discussed herein were chosenand described in order to explain the principles and the nature ofvarious example embodiments and its practical application to enable oneskilled in the art to utilize the example embodiments in various mannersand with various modifications as are suited to the particular usecontemplated.

In the drawings and detailed description, there have been disclosedexemplary embodiments. However, many variations and modifications can bemade to these embodiments. Accordingly, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the embodiments being definedby the following claims.

The invention claimed is:
 1. A method, performed by a user equipment ina wireless network, the method comprising: receiving informationindicating Random Access Channel (RACH) physical resources, saidinformation indicating a set of RACH physical resources for transmissionof a random access preamble for random access attempts that use a firstnumber of repetitions of the random access preamble for each randomaccess attempt; and transmitting, for a single random access attempt, arandom access preamble with the first number of random access preamblerepetitions using at least the set of RACH physical resources, whereinthe transmitted random access preamble with the first number of randomaccess preamble repetitions is transmitted according to a frequencyhopping pattern, and wherein a starting frequency location of thefrequency hopping pattern is randomly selected by the user equipment. 2.The method of claim 1, wherein the frequency hopping pattern allowsmultiplexing in time and frequency with a frequency hopping pattern ofanother user equipment.
 3. The method of claim 1, wherein thetransmission power of the random access preamble to be transmitted isbased at least on the first number of random access preamblerepetitions.
 4. The method of claim 1, wherein a starting point, for arandom access attempt, is based at least on the first number of randomaccess preamble repetitions.
 5. The method of claim 1, furthercomprising: transmitting, for a retry random access attempt, a randomaccess preamble with a retry number of repetitions if the single randomaccess attempt is not successful.
 6. The method of claim 1, wherein theretry number of repetitions is greater than the first number ofrepetitions.
 7. The method of claim 6, wherein the retry random accessattempt is a next random access attempt or a periodically re-occurringsub-sequent retry random access attempt.
 8. The method of claim 1,wherein the received information is indicated in a system informationblock message broadcasted by a radio network node.
 9. The method ofclaim 1, wherein the RACH physical resources correspond to OrthogonalFrequency-Division Multiplexing (OFDM) physical resources, and whereinthe random access preamble to be transmitted is randomly selected from aplurality of random access preambles for contention-based access.
 10. Awireless device for a wireless network, the wireless device comprising:a communication unit configured to communicate with a network node in acell of said wireless network, and; processing circuitry configured tocause the wireless device to: receive information indicating RandomAccess Channel (RACH) physical resources, said information indicating aset of RACH physical resources for transmission of a random accesspreamble for random access attempts that use a first number ofrepetitions of the random access preamble for each random accessattempt; and transmit, for a single random access attempt, a randomaccess preamble with the first number of random access preamblerepetitions using the set of RACH physical resources, wherein thetransmitted random access preamble with the first number of randomaccess preamble repetitions is transmitted according to a frequencyhopping pattern, and wherein a starting frequency location of thefrequency hopping pattern is randomly selected by the user equipment.11. The wireless device of claim 10, wherein the frequency hoppingpattern allows multiplexing in time and frequency with a frequencyhopping pattern of another user equipment.
 12. The wireless device ofclaim 10, wherein the transmission power of the random access preambleto be transmitted is based at least on the first number of random accesspreamble repetitions.
 13. The wireless device of claim 10, wherein astarting point, for a random access attempt, is based at least on thefirst number of random access preamble repetitions.
 14. The wirelessdevice of claim 10, wherein the processing circuitry is furtherconfigured to cause the wireless device to: transmit, for a retry randomaccess attempt, a random access preamble with a retry number ofrepetitions if the single random access attempt is not successful. 15.The wireless device of claim 14, wherein the retry number of repetitionsis greater than the first number of repetitions.
 16. The wireless deviceof claim 15, wherein the retry random access attempt is a next randomaccess attempt or a periodically re-occurring subsequent retry randomaccess attempt.
 17. The wireless device of claim 10, wherein thereceived information is indicated in a system information block messagebroadcasted by a radio network node.
 18. The wireless device of claim10, wherein the RACH physical resources correspond to OFDM physicalresources, and wherein the random access preamble to be transmitted israndomly selected from a plurality of random access preambles forcontention-based access.
 19. A method, performed by a user equipment ina wireless network, the method comprising: receiving informationindicating Random Access Channel (RACH) physical resources, saidinformation indicating a set of RACH physical resources for transmissionof a random access preamble for random access attempts that use a firstnumber of repetitions of the random access preamble for each randomaccess attempt; and transmitting, for a single random access attempt, arandom access preamble with the first number of random access preamblerepetitions using the set of RACH physical resources, wherein thetransmission power of the transmitted random access preamble is based atleast on the first number of random access preamble repetitions.